FECUNDATION. 183 
Fig. 279 is a section of the stigma, style, and ovary, and is 
intended to point out the long course followed by the pollen-tubes 
in penetrating from the 
stigma to the interior of 
the ovary, where each of 
them comes in contact 
with the ovules. 
One of these ovules is 
represented in Fig. 276, 
taken singly and magni- 
fied, to show this pheno- 
menon more clearly. The 
ovule here represented is 
that of viola tricolor. The 
extremity of the pollen- 
tube, in contact with the 
summit of the ovule, pro- 
ceeds to place itself in still 
nearer connexion with one 
of the constituting cells 
of this nucleus, now ex- 
cessively developed, in 
which state it bears the 
name of the embryo-sac, 
because there the embryo 
is fully developed and 
ready to burst. The same 
organ is represented, at 
the moment of fecunda- 
tion, in Fig. 277. Here 
an internal section of the 
Fig. 279.—Fecundation of the Ovule. 
ovule of the Polygonum is given, both before and after fecun- 
dation; a is the ovule before fecundation, 3, Fig. 278, the same 
organ after it. We see on the fecundated ovule sp, the com- 
mencement of the formation of the embryo-sac, at the terminating 
point of the pollen-tube. 
About the year 1837, two German botanists, MM. Schleiden 
and Horkel, announced that the vegetable embryo pre-exists as a 
